The present invention is directed to an apparatus for manufacturing constrictions in fibers with the apparatus having a stretching device for stretching the fibers by applying a tensile force thereto and a heating installation for brief local heating of a stretched fiber to a softening temperature at which a permanent constriction is formed in the fiber. The tensile force produced in the fiber by the stretching device and the brief local heating are so matched to one another that a constriction is formed in the fiber without tearing or pulling the fiber apart.
For optical communication with monomode glass fibers, transmitting modules are required which modules achieve as high as possible an input coupling efficiency of a laser beam from a semiconductor laser into the monomode glass fiber. A possible coupling optics is a conically tapering fiber end section which is called a tapered end has been heated to form a round lens on the end. Such coupling optics or arrangements are discussed in an article by H. Kuwahara et al, "Efficient Coupling from Semiconductor Lasers into Single-Mode Fibers with Tapered Hemispherical Ends", Applied Optics, Vol. 19, No. 15, Aug. 1, 1980, Pages 2578-2583.
To this end, the fiber is, for example, stretched and heated locally by an electrical arc of an arc welder until the attainment of a softening point so that it becomes permanently constricted in the softened region. The cooled constricted fiber is severed approximately at the narrowest point of the constriction and the end of a thus obtained taper is in turn convexly glazed into a lens by use of the arc welder. The point at which the severing is effected in the constriction is fixed by the laser parameters and the fiber parameters which are given by the far field angle of the laser and the core diameter, cladding diameter and refractive index step or jump between the core and cladding for the fiber.
In order to obtain a high coupling efficiency between the laser diode and the monomode or single mode glass fiber to be coupled thereto with as simple as possible an adjustment in which no angular adjustments need be carried out, a far-field distribution, which is symmetrical to the fiber axis, of the coupling optics consisting of a taper with the fused or melted-on lens is necessary. It is to be understood that the far-field distribution of the coupling optics is the far-field of light emerging from the lens at the end of the taper when input coupling is effected via the opposite fiber end. A far-field distribution symmetrical to the fiber axis can be achieved by means of a taper which is as rotationally symmetrical as possible.